1. Field of the Invention
The present invention relates in general to diaphragm actuator valves, and more particularly to an adjustable actuator spring associated with the diaphragm actuator valve. Still more particularly, this invention relates to an adjustable keeper element that is used in conjunction with the actuator spring to adjust the tension on the valve.
2. Description of the Prior Art
Valve control devices are vital to many industries, in particular to the oil and gas industry where large volumes of fluid or gas under varying pressures must be controlled through pipelines. Diaphragm actuator valve devices are the most common valve control devices used. These devises employ a flexible pressure responsive element as a diaphragm. The diaphragm is typically sandwiched between two halves of a housing, creating an open space above and below the diaphragm. An actuator stem or plunger stem extends from the diaphragm, being associated with the diaphragm in such a way as to move up or down relative to the movement of the flexible diaphragm.
The diaphragm can be controlled by controlling the pressure on either side of the diaphragm. By increasing the pressure in the space above the housing a direct-acting actuator is created. By controlling the pressure below the diaphragm a reverse-acting actuator is created. In either case, a compression spring, or actuator spring, is used to create tension between the diaphragm's movement and the movement of the valve plug coupled to the end of the plunger stem. A pneumatic signal operates upon the diaphragm to cause the plunger stem to open and close the valve plug, thus controlling liquid or gas flow through a pipe. Control of the valve plug against the valve seat is vital in maintaining adequate control of fluid flow through a pipe. Some examples of this type of valve control device are Plotkin et al. (U.S. Pat. No. 3,428,063), and Bauer (U.S. Pat. No. 4,098,487).
One of the problems of these types of valve control devices is in adapting the device to control the large range of pressures encountered. Simply specifying a valve size to match an existing pipeline size leaves much to chance and will likely create an impractical situation in terms of adequate control. A valve which is too small will not pass the required amount of flow. A valve that is too large will be unnecessarily expensive and may create instability problems as it attempts to control very low increments of plunger travel. In the past, these types of valves have been fine tuned for the specific intended application by changing out the valve plug and/or valve seat.
One invention is directed towards a means of adjusting the pressure exerted on the valve plug and valve seat. Reinicke et al. (U.S. Pat. No. 4,309,022) disclose a valve that applies a high force to the valve plug momentarily to seat the plug, then a lower pressure to maintain the seating. This invention is primarily directed towards improving the long-term usefulness of valve plugs and valve seats that otherwise become damaged due to creeping of the valve seat and plug material under pressure.
An alternative to controlling the tension on the valve plug and valve seat is to adjust the actuator spring tension. This is presently accomplished by one of two methods. The first is adjusting a spring adjustor attached to the bottom end of the spring, forcing it either up against the diaphragm or away from the diaphragm. The second is by replacing the spring with a spring of the desired tension. The first method offers only very small changes in tension control, while the second is cumbersome and time consuming. A device that could control the sensitivity of the valve, thus adapting to various changes in liquid flow and pressure, is desirable.